1. Field Of The Invention:
This invention pertains to devices utilized for purposes of measuring the position and orientation of receiving antennae with respect to transmitting antennae using direct current signals.
2. Description Of the Prior Art:
The art of using transmitting and receiving components with electromagnetic coupling for measuring position and orientation is well known especially with respect to armament sighting systems where the receiver component would be located in a gunner's helmet and a transmitter component would be attached to a nearby electrically non-conductive structure. As the gunner would sight-in a target through a sighting cross-hair affixed to his helmet, the receiver located thereupon would pick up signals generated by the transmitter. These signals would then be processed by a computer to determine the position and orientation of the helmet and then to contemporaneously point a unit of armament in the same direction as the helmet mounted sight piece.
As taught in U.S. Pat. No. 4,054,881 issued Feb. 18th, 1977 to Raab and U.S. Pat. No. 4,287,809 issued Sept. 8th, 1981 to Egli et al., and U.S. Pat. No. 4,314,251 issued Feb. 2nd, 1982 to Raab and U.S. Pat. No. 4,396,885 issued Aug. 2nd, 1983 to Constant, an alternating current (AC) signal is applied in a time division or frequency division format to a transmitter consisting of two or three orthogonal coils which generate an AC electromagnetic field which is measured by an AC receiver likewise consisting of three or two orthogonal coils. These sensed signals are then filtered and amplified in a method compatible with the transmitted format, converted to a digital format and then read into a computer where various mathematical methods are resorted to in order to extract position and orientation with resort to applicable electromagnetic field equations.
All current systems such as the ones abovesaid that utilize an AC transmitted signal work accurately only when there are no electrically conductive materials located near either the transmitter or receiver because any transmitted AC signal would invariably induce eddy currents in these conductive materials which would in turn serve to generate an AC magnetic field that would distort any transmitted field, and, of course, any ultimate output position and orientation data. In fighter aircraft or helicopters where it is desired to use these position and orientation measuring systems, there are a lot of highly conductive materials in the form of aluminum, titanium, magnesium, stainless steel, and copper used in the construction of the cockpit structure, seat, wiring and helmet-mounted displays. U.S. Pat. No. 4,287,809 teaches a method of compensating for the errors resulting from any field distortion due to cockpit metal that does not move with respect to the transmitter. The compensation method therein suggested involves making measurements throughout the cockpit to determine the amount of such distortion and then using this data to form a correction that is applied to the sensed signals. In a similar manner, U.S. Pat. No. 4,394,831 issued July 26th, 1983 to Egli et al. teaches a method to accomplish compensation for errors due to eddy currents induced in metal such as would be found in a display located on a pilot's helmet. This compensation method again requires initial experimental measurements of such distortion in order to effect necessary corrections and provides moderate improvements in accuracy only when the amount of metal on the helmet is concentrated in a single location and the helmet does not go through large angular rotations or translations in the cockpit. These types of compensation efforts that are required to make AC systems work accurately are time consuming and expensive to perform and only work in environments where there would not be too much conductive material near transmitter or receiver units. In many helicopters, for example, AC systems cannot be utilized at all because the distortions produced are simply too large to be corrected merely by such mapping.
The instant device represents a radical departure from all of the prior art relating to such transmitting and receiving position and orientation devices, insomuch as it avoids, in-toto, resort to AC signals and instead relies upon DC signals. Such reliance on DC signals obviates completely any need for a priori calibration undertakings and greatly expands the potential utility of devices of this type. Moreover, manufacture and utilization of this device for purposes of accomplishing all that current devices can accomplish is manifestly less expensive than such manufacture and utilization of said currently used devices are or ever will be.